The present invention relates to electrical cable connector devices and, more particularly, to such a device of the plug and socket type having a locking mechanism to insure secure connections. Such devices may find particular application in high accuracy measuring devices utilizing disposable measurement probes, or in any situation where a low cost, high reliability cable connection capable of frequent connection and disconnection is desirable.
In designing electrical cable connectors, it is frequently necessary to insure a mechanically secure connection by including a locking mechanism for the connector. Such a mechanism is particularly helpful in preventing accidental disconnections due to inadvertent bumping, pulling or vibration of the connector. Additionally, a strain relief is often required to reduce strain upon the point of attachment of the cable to the connector, so as to reduce the possibility of separating the cable from the connector.
Typically, low cost connectors are produced by using relatively large tolerances or less expensive materials. Such connectors rely on interlocking tabs on the connector shells to provide a locking mechanism, and/or snap-on clasps to provide strain relief. Because of the use of less expensive materials, typically including contact pins of non-noble metals, high contact resistance is introduced, resulting in low reliability.
High contact resistance is particularly objectionable in connectors for use with high accuracy measuring devices. One possible solution in such cases is the use of large surface areas for electrical contact. This not only results in the use of more material, thereby increasing cost, but also greatly increases the overall size of the connector assembly, making such a connector bulky and awkward to use.
Generally, with presently known connectors, high reliability requirements necessitate the use of a connector of relatively high cost. Such connectors as are typically used with high accuracy measuring devices include those of the MS Series, using solder or crimp pins with a metal housing and nut assembly. MS Series connectors normally require external strain relief and contain from six to fifteen parts in addition to the connector pins. Consequently, such connectors are both relatively large and costly. Additionally, the mating action, which is either twist lock or screw lock, is typically slow to perform.
High reliability locking connectors have also long been necessary for attaching printed circuit boards to the chassis of the device in which they are used. Typical of such connectors are those shown in U.S. Pat. No. 3,216,580 and U.S. Pat. No. 4,008,942. The printed circuit board is inserted into a socket so as to engage a set of contacting members. A locking mechanism is provided generally through the use of locking members extending from the socket along the edges of the circuit board. In the '580 patent, the members are made of a semi-flexible plastic material and have a protrusion at the free end of each. Each protrusion is fittable within a notch in the edge of the board so as to lock the board into place. In the +942 patent, the members are made of spring steel, and are bent such that each forms a crook engageable with a notch in the edge of the board.
While such connectors are generally of high reliability, they are not suitable for use in low cost cable connections. Such connectors are by nature large and bulky, since the printed circuit boards for which they are design are quite large in comparison with a cable. Additionally, the use of locking members extending from the socket add to the size of the connector, as well as the complexity of its manufacture. Moreover, a circuit board connector must be designed so as to facilitate air circulation around the board and its components, whereas cable connections must be completely insulated.
Similarly, high reliability connectors are known for use with flat ribbon cables associated with printed circuit boards. As shown in U.S. Pat. No. 3,149,897 and U.S. Pat. No. 3,737,833, such connectors typically comprise a plug and socket arrangement. A locking mechanism is provided, as in the circuit board connectors, wherein locking members extend outwardly from the socket along the plug edges and engage with notches or projections defined along the edges of the plug. Such connectors tend to be bulky, however, in part due to their use with relatively large ribbon cables, but also due to the use of locking members extending outwardly from the socket. Such connectors require low tolerances and a relatively large number of parts, thereby increasing their cost. Further, especially when the connector is in a disconnected state, the exposed, protruding locking members are subject to bending or breakage.
It is seen, therefore, that a high reliability, low cost electrical cable connector is needed. Such a connector should be of relatively small size, and form a connection that is mechanically secured. A strain relief should be provided. Moreover, the connector should be capable of repeated connections and disconnections without risk of damage to the connector.